A. Field of Invention
The present invention relates to high intensity discharge (HID) lamps. One type of HID lamp of particular interest is metal halide (MH) arc lamps, whether jacketed or unjacketed.
B. Problems in the Art
Larger lighting fixtures, like sports field lights 2 (see, e.g., FIGS. 1 and 2) use very high wattage HID (High Intensity Discharge) lamps 4 to generate high-intensity light to travel the substantial distances from the fixtures to the field 5. The cost of such lighting is substantial. The light fixtures usually must be elevated, on cross arms 7 on poles 6 or other structures, which is costly. Sometimes the poles must be located a substantial distance from the field, e.g. because of spectator stands 8 surrounding the field. A limited number of fixtures can be elevated per pole because of wind load and other factors. Therefor, the more fixtures required to adequately light a filed, the more cost of not only fixtures, but structure to elevate them, which can represent a significant part of the total cost of a system as shown in FIG. 1. Also, each lamp and fixture adds expense; namely structure and electrical cost to operate.
Thus, a continued goal for such fixtures is to improve economy and efficiency. One way is to get more light out of each fixture. It then might be possible to reduce the total number of fixtures, which would result in less cost to elevate and to electrically power the whole set of lights. Many times, there are 30, 40, or more fixtures. A reduction by 10 or 15 fixtures could result in huge savings.
Another approach at getting more light to the sports field with fewer fixtures is to use larger wattage lamps. Larger wattage lamps can pump out more light energy per fixture. Traditional sports lighting lamps can be in the 500 to 1500 watt range. There are now available HID arc lights in the 2000-watt range.
One example of a 2000 watt sports lighting fixture is disclosed in co-pending U.S. Ser. No. 10/072,703, incorporated by reference herein. The basic structure of such a fixture is illustrated at FIG. 2. A bowl-shaped reflector 30, with a glass lens 31, surrounds a 2000 watt MH arc lamp 12. Mounts 22L and 22R allow arc tube 12 (unjacketed) to be removably placed into the position shown. Reflector 30 and the parts within are connected to a mounting mogul or housing 3 (here with an integrated ignitor circuit), which in turn is adjustably connected to a mounting elbow 4. Elbow 4 can be mounted to a cross arm 7 or other structure. The fixture 2 can thus be elevated by suspension from such a cross arm, but can be adjusted relative the cross arm to aim it to a certain location or direction relative the field.
However, although such high-powered lamps are available, there is still room for improvement. The nature of arc lamps is that most lose light output over time. They are brightest over a first period of time (for 1000-2000-watt fixtures, approximately the first 100 hours of operation). It is believed that there is a gradual reduction in light output as chemicals inside the arc precipitate out or migrate and interact with chemicals in the quartz or other parts of the light structure. During this initial period, on the order of 25% loss of light output can occur.
Then, over a second period (the remaining lamp life), a further gradual reduction in light output can and usually does occur. By the end of conventional lamp life (many times several hundred hours) there can be on the order of an additional 50% light loss or depreciation. Thus, by the end of conventional lamp life, combined light depreciation from those two periods of time, can be on the order of one-third to one-half of the original light output.
Therefore, most sports lighting systems, which have to maintain certain level of quantity and quality of light across the filed, are designed to have an excess number of light fixtures. This results in higher initial cost and initial inefficiency of excess light, but hopefully produces enough light over time despite the light depreciation problem discussed above.
If one reduces the number of fixtures designed or relied upon for lighting a field because of use of higher wattage lamps, the light depreciation described above, over time, may reduce total light output below what is required, desired, or designed for that particular field. It is usually not an answer to replace the lamps after only 50 hours or less of operation time because it is too expensive (these lamps can cost tens, if not hundreds, of dollars apiece). Thus, to insure adequate lighting levels, even toward the end of normal lamp lifetime, most lighting system designers add additional light fixtures, which of course, adds back cost into the system and is counter to the goal of increasing economy.
It is therefore an object, feature, or advantage of the present invention to provide an apparatus and method directed to stopping or reducing the light output loss or depreciation over the life of these types of lamps. It is believed that at least a portion of light depreciation is the result of uneven temperature around the quartz arc tube that encases the arc.
The basic structure of this type of arc tube source is shown at FIG. 3, and is well known in the art. A quartz arc tube 12 has a sealed interior chamber, which contains certain chemicals. Two electrodes 14 extend into opposite ends of the hollow interior chamber of arc tube 12. Part of each electrode 14 is encased in an associated pinched end 16 of arc tube 12. Pinched ends 16 can be mounted in insulators (e.g. ceramic) 18. Electrodes 14, or conducting members (e.g. metal ribbon) connected to electrodes 14, extend into or through insulator 18. The opposite pinched ends 16 of arc tube 12 are sealed to or mounted in members 18. Electrical energy is supplied to arc tube 12 through high temperature electrical leads (not shown) that extend into insulators 18 and are in electrical communication with electrodes 14.
During operation, electrical power is supplied to electrodes 14. An electrical arc forms between electrodes 14 inside of arc lamp 12. In the operative position shown in FIG. 3 (horizontal), arc stream 20 usually “arcs” such that its middle section is closer to the top of the arc tube 12 than to the bottom. It appears this phenomenon results in unequal temperature between top and bottom of arc tube 12. Heat energy from arc stream 20 heats the top of arc tube 12 hotter than the bottom. Many times the difference can be substantial; e.g., approximately 1000° C. temperature at the top and 600° C. temperature at the bottom of arc tube 12.
This unequal temperature is believed to result in at least some of the chemicals in arc tube 12 finding cooler parts of the arc tube. They can precipitate out and, thus, reduce light output because they are no longer active chemicals in the generation of the arc stream and/or precipitate out and deposit on the inside of the arc tube 12 and actually block light from escaping from arc tube 12.
Another phenomenon which is believed to occur is that the unequal temperature may cause some of the chemicals in the quartz to migrate into the interior open space of the arc tube and combine with the chemicals inside the arc tube in a manner that removes them from light generation and/or results in light blocking deposits.
Therefore, a goal, object, feature and/or advantage of the invention is to attempt to reasonably equalize the temperature around the entire quartz arc tube 12 to reduce temperature differential between parts of the arc tube 12. This will also be called attempting to promote isothermal conditions all around the arc tube.
Other objects, features, and/or advantages of the present invention include an apparatus and method which:                a. Promotes temperature of at least a part of an arc tube to enhance performance of the arc tube and/or lamp associated with the arc tube;        b. Promotes temperature of at least a part of an arc tube to prolong operational life of the arc tube or lamp associated with the arc tube;        c. Allows adjustment of operating characteristics, structure, or components of arc tube to increase or maximize light output and maintenance of light output over the operating life of the arc tube or lamp associated with it, while reducing detrimental or deteriorating effects of such increase or maximization;        d. Improves maintenance of light output over time when operating an arc tube;        e. Is relatively economical, efficient, flexible, and durable.        
These and other objects, features, and/or advantages of the invention will become more apparent with reference to the accompanying specification and claims.